I now see where InnoDB is maintaining the count in 5.1. So I guess it
is probably necessary, although I cannot reproduce a case where
handlerton->commit/rollback is not being called.
On Fri, Feb 25, 2011 at 7:06 PM, Zardosht Kasheff <zardosht@stripped> wrote:
> Hello Konstantin,
> Thanks for your reply. It is the 5.1 case that I am particularly
> interested in. I do not see where InnoDB is maintaining this count and
> auto committing the transaction.
> Also, I always see handlerton->commit/rollback being called at the end
> of statement. This is what I did for the simplest example:
> create temporary table foo (a int);
> Lock tables foo read;
> select * from foo;
> unlock tables;
> I saw innobase_commit get called during "lock tables foo read" and
> during "select * from foo;"
> So I guess I still dont see an example where
> handlerton->commit/rollback is not called. Is there a chance this has
> been fixed in 5.1 as well?
> On Fri, Feb 25, 2011 at 6:57 PM, Konstantin Osipov
> <kostja.osipov@stripped> wrote:
>> * Zardosht Kasheff <zardosht@stripped> [11/02/26 02:41]:
>>> In ha_ndbcluster::external_lock, in mysql 5.1.52, I see the following
>>> comment under the case where lock_type == F_UNLCK:
>>> Unlock is done without a
> transaction commit / rollback.
>>> This happens if the thread didn't
> update any rows
>>> We must in this case close the
> transaction to release resources
>>> But I do not see this anywhere else in any other handler.
>>> Is there a scenario where a transaction that has been registered via
>>> trans_register_ha does NOT have handlerton->commit or
>>> handlerton->rollback getting called, and therefore requireing
>>> ha_ndbcluster::external_lock to execute:
>>> thd_ndb->trans= NULL;
>> In 5.5 handlerton->commit/rollback is guaranteed to be eventually
>> called for any registered handler.
>> However, this doesn't always happen in order.
>> One example, when ha->external_lock(F_UNLCK) is called before
>> handlerton->commit/rollback is mysql_unlock_some_tables and
>> MySQL can call these functions before end of statement,
>> (commit/rollback is done at end of statement), and they
>> in turn call handler::external_lock.
>>> My guess is that no, this is not required, otherwise other storage
>>> engines would do this, but I would like to confirm.
>> InnoDB counts calls to external_lock(F_LOCK) and
>> external_lock(F_UNLOCK). When it drops to zero, it auto-commits
>> the statement transaction. This is necessary in 5.0 and 5.1,
>> where handlerton->commit/rollback is not guaranteed to be called
>> at end of statement (try, for the simplest example, to create a
>> temporary table and lock it with LOCK TABLES, and then execute
>> some statements).